Correct. Fan dipoles work because the resonant 1/4-wave elements are lower impedance than the non-resonant elements, so they get the majority of the power. A neat trick, really.
The LNR End-Fedz antennas use traps. They appear to work just fine. wunder K6WRU Walter Underwood CM87wj http://observer.wunderwood.org/ (my blog) > On Feb 11, 2017, at 12:50 PM, K9MA <[email protected]> wrote: > > On 2/11/2017 13:03, Brian Pietrzyk wrote: >> Now comes the fantasy thinking... What about making it an end fed multi band >> by either putting traps in the 80m end fed or better still adding on a >> couple of fan EFHW wires for 40 and 20? Anyone tried this? How would the >> efficiencies compare to their centre fed trap or fan dipole counterparts >> respectively? > > That won't work, because the shorter wires will present a much lower > impedance, and essentially short out the half wave wire. The whole idea of > the EFHW is that the high feedpoint impedance reduces ground system current > to practically zero. > > A trap might work, but might not be compatible with keeping the antenna very > light. A QRP trap could be pretty small, I suppose, but it still might be > hard to support the wire with the extra weight on it using a lightweight pole. > > However, an EFHW will work on harmonics, though the pattern changes. A 40 > meter half wave works quite well on 20, but I'm not sure an 80 meter half > wave would be all that great on 20, especially with a single support. The > free space patterns of long wire antennas are shown in the ARRL Antenna Book. > As frequency goes up, more lobes appear in the pattern, and the main ones > get closer to the axis of the wire. For example, a full wave antenna has a > cloverleaf pattern, the lobes about 55 degrees from the wire axis, with nulls > broadside. For a 2 wavelength wire, there are 8 lobes, the main ones 35 > degrees from the wire axis. These patterns will, of course, be modified by > the effects of ground and the fact that the wire probably won't be straight, > but the free space patterns give some idea of how the antenna will radiate. > Modeling these antennas is very easy, and gives much more accurate results. > > Note that the pattern of an EFHW (full wave, etc.) is NOT the same as that of > a center fed dipole operated at even harmonics. > > 73, > > Scott K9MA > > > -- > Scott K9MA > > [email protected] > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [email protected] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
